Getting a forged 383 built and I'm continuing to struggle with piston cc. I wanted to do flat tops (-5) but my builder is pushing hard for -12s. I will be running ported lt4 heads with 54cc chambers. I was hopping to get close to 12:1 but dish would put it closer to 10:5. Only having an issue because the builder had done a ton of lt1s and says I will not be happy with the higher compression.

Thoughts?

 

10.5 is stock compression. Id shoot for close to 12.1 like you want. Why is he suggesting less compression?

 

The 12cc dish piston. With 54cc heads, 3.75 stroke, 4.03 piston snd quench of .039. Will give you 11.5 compression tho. With the 5cc pistons and everything else same. It will be 12.6.

 

I think you're right. He was concerned about getting it to run on 93 octane. He's more than willing to build it either way. Just wanting some opinions.

Thank you!

 

The LT4 was 10.8 stock....

 

LT1's run great on 12:1. There are other sizes than -5 and -16. My dad's 383 runs with -8cc Probe 2618 pistons and the one he's building has -7.5cc wiseco 2618 pistons.

 

2618 pistons are a bad choice for a normal street/strip build, 4032 is preferred because it is a little harder and the ring lands will last a lot longer.

 

I have no worries using 2618 pistons, they are plenty hard.

 

For how long?
I have been told by 20k miles ring lands can be worn enough to compromise ring seal. To me that is not long enough for a street/strip car, plus extra noise......

 

If your builder is saying that an LT1 wont run on pump gas with 11.5:1, then he has never built a 92-97 LT1, hes probably used to the 70s LT1s.

 

If you're not planning on running any forced induction then get the flat tops with 5cc valve relieves. For a lt1 na 383 12:1 is a great compression